In an LTE system, connection states between a user apparatus UE (to be referred to as UE hereinafter) and a base station eNB (to be referred to as eNB hereinafter) are indicated by two states of an RRC (Radio Resource Control) idle state (RRC_Idle) and an RRC connected state (RRC_Connected).
When a UE connects to a network, a UE context is generated by an MME (Mobility Management Entity) in a core network (core NW) side, so that the UE context is held by an eNB that the UE is connected to and by the UE. Note that the UE context is information including bearer related information and security related information and the like.
When the UE transits between the RRC idle state and the RRC connected state, a lot of signaling of call control including the core NW side occurs. Thus, how signaling can be decreased is a problem.
For example, when a UE is caused to transit from an RRC connected state to an RRC idle state, signaling shown in FIG. 1 occurs (non-patent document 1 and the like). The case shown in FIG. 1 is a case where an eNB 2 detects that communication of a UE 1 does not occur for a predetermined time, and disconnects connection with the UE 1 to cause the UE 1 to transit to an RRC idle state.
In FIG. 1, the eNB 2 transmits a UE context release request (UE Context Release Request) to an MME 3 (step 1). The MME 3 transmits a bearer release request (Release Access Bearers Request) to an S-GW 4 (step 2), and the S-GW 4 returns a bearer release response (Release Access Bearers Response) to the MME 3 (step 3).
The MME 3 transmits a UE context release instruction (UE Context Release Command) to the eNB (step 4). The eNB 2 transmits an RRC connection release (RRC Connection Release) to the UE 1 (step 5) to cause the UE 1 to transit to an RRC idle state. Also, the eNB 2 releases the UE context and transmits a UE context release complete (UE Context Release Complete) to the MME 3 (step 6).